topology won't install on PostgreSQL 9.2beta1

Description

Breaks on this line:

ALTER DOMAIN topology.TopoElement DROP CONSTRAINT type_range;

with error:
constraint "type_range" of domain "topology.topoelement" does not exist

I'm surprised this works on older versions it seems older versions of PostgreSQL simply ignore this line if the constraint doesn't exist so I can run that an infinite number of times on older without warning. So i suspect this is a bug fix in 9.2.